Given　the　Mayers-Lo-Chau　(MLC)　no-go　theorem,　unconditionally　secure　quantum　bit　commitment　(QBC)　is　impossible　and　hence　quantum　oblivious　transfer　(QOT)　based　on　QBC　is　insecure.　In　this　paper,　we　propose　a　secure　all-or-nothing　QOT　protocol　and　a　one-out-of-two　QOT　protocol　respectively.　The　unique　merit　of　the　proposed　protocols　lies　in　that　it　is　not　based　on　QBC　but　based　on　an　untrusted　third　party.　Moreover,　the　proposed　protocols　do　not　violate　Lo＇s　no-go　theorem　so　that　their　security　can　be　achieved.　(C)　2014　Elsevier　GmbH.　All　rights　reserved.